A Tetradentate Ligand Enables Iron-Catalyzed Asymmetric Hydrogenation of Ketones in a CO- or Isocyanide-Free Fashion.

We herein reported the design and synthesis of a ferrocene-based tetradentate ligand that is featured with modular synthesis and rigid skeleton. Its iron(II) complex facilitates asymmetric direct hydrogenation of ketones without the participation of extra strong-field ligand such as CO and isocyanide. Hydride donor lithium aluminum hydride (LAH) converted non-reactive Fe(II) species to reactive Fe(II) hydride species. With this catalyst, various chiral alcohols including the intermediate for montelukast could be prepared with satisfactory yields and enantioinduction.

A 13-million turnover-number anionic Ir-catalyst for a selective industrial route to chiral nicotine.

Developing catalysts with both useful enantioselectivities and million turnover numbers (TONs) for asymmetric hydrogenation of ketones is attractive for industrial production of high-value bioactive chiral entities but remains a challenging. Herein, we report an ultra-efficient anionic Ir-catalyst integrated with the concept of multidentate ligation for asymmetric hydrogenation of ketones. Biocatalysis-like efficacy of up to 99% ee (enantiomeric excess), 13,425,000 TON (turnover number) and 224 s-1 TOF (turnover frequency) were documented for benchmark acetophenone. Up to 1,000,000 TON and 99% ee were achieved for challenging pyridyl alkyl ketone where at most 10,000 TONs are previously reported. The anionic Ir-catalyst showed a novel preferred ONa/MH instead of NNa/MH bifunctional mechanism. A selective industrial route to enantiopure nicotine has been established using this anionic Ir-catalyst for the key asymmetric hydrogenation step at 500 kg batch scale, providing 40 tons scale of product.

Enantioselective semisynthesis of novel cephalotaxine esters with potent antineoplastic activities against leukemia.

Cephalotaxine-type alkaloids (CTAs), represented by homoharringtonine (HHT, 1), display potent efficacy against different types of leukemia cells. In this study, a method for hydrogenation of ß-substituted itaconic acid monoesters with chiral Ru[DTBM-SegPhos](OAc)2 was developed. This metal-catalyzed asymmetric hydrogenation enabled the convenient semisynthesis of novel cephalotaxine derivatives with chiral 2'-substituted-succinic acid 4-mono-methyl esters as side chains. The preliminary structure-activity relationship (SAR) of the compounds' antineoplastic activities was studied. Eventually, we discovered compound 10b with potent antineoplastic activities against leukemia and broadly anticancer activities against a panel of cancer cells. Our study provided a highly enantioselective process enabling the semisynthesis of cephalotaxine derivatives, which are interesting for further study on a scientific basis.

The adenosine analog prodrug ATV006 is orally bioavailable and has preclinical efficacy against parental SARS-CoV-2 and variants.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus driving the ongoing coronavirus disease 2019 (COVID-19) pandemic, continues to rapidly evolve. Because of the limited efficacy of vaccination in prevention of SARS-CoV-2 transmission and continuous emergence of variants of concern (VOCs), orally bioavailable and broadly efficacious antiviral drugs are urgently needed. Previously, we showed that the parent nucleoside of remdesivir, GS-441524, has potent anti-SARS-CoV-2 activity. Here, we report that esterification of the 5'-hydroxyl moieties of GS-441524 markedly improved antiviral potency. This 5'-hydroxyl-isobutyryl prodrug, ATV006, demonstrated excellent oral bioavailability in rats and cynomolgus monkeys and exhibited potent antiviral efficacy against different SARS-CoV-2 VOCs in vitro and in three mouse models. Oral administration of ATV006 reduced viral loads and alleviated lung damage when administered prophylactically and therapeutically to K18-hACE2 mice challenged with the Delta variant of SARS-CoV-2. These data indicate that ATV006 represents a promising oral antiviral drug candidate for SARS-CoV-2.

Iridium-Catalyzed Hydroiodination and Formal Hydroamination of Olefins with N-Iodo Reagents and Molecular Hydrogen: An Umpolung Strategy.

We herein report a convenient method to convert olefins to organic iodides and amines using an Ir/ZhaoPhos catalyst, molecular hydrogen, and an electrophilic iodine(I) reagent. High yields and regioselectivities were obtained under mild conditions. In addition, basic workup with potassium carbonate leads to C-N products. Control experiments and DFT calculations tentatively excluded the pathway involving the in situ formation of HI. Instead, a catalytic cycle involving the hydrogenation of the haliranium ion intermediate was proposed.

Remdesivir Metabolite GS-441524 Effectively Inhibits SARS-CoV-2 Infection in Mouse Models.

The outbreak of coronavirus disease 2019 (COVID-19) has resulted in a global pandemic due to the rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). At the time of this manuscript's publication, remdesivir is the only COVID-19 treatment approved by the United States Food and Drug Administration. However, its effectiveness is still under question due to the results of the large Solidarity Trial conducted by the World Health Organization. Herein, we report that the parent nucleoside of remdesivir, GS-441524, potently inhibits the replication of SARS-CoV-2 in Vero E6 and other cell lines. Challenge studies in both an AAV-hACE2 mouse model of SARS-CoV-2 and in mice infected with murine hepatitis virus, a closely related coronavirus, showed that GS-441524 was highly efficacious in reducing the viral titers in CoV-infected organs without notable toxicity. Our results support that GS-441524 is a promising and inexpensive drug candidate for treating of COVID-19 and other CoV diseases.

Nickel-Catalyzed Asymmetric Hydrogenation of Cyclic Alkenyl Sulfones, Benzo[b]thiophene 1,1-Dioxides, with Mechanistic Studies.

A highly efficient catalytic system based on the cheap transition metal nickel for the asymmetric hydrogenation of challenging cyclic alkenyl sulfones, 3-substituted benzo[b]thiophene 1,1-dioxides, was first successfully developed. A series of hydrogenation products, chiral 2,3-dihydrobenzo[b]thiophene 1,1-dioxides, were obtained in high yields (95-99%) with excellent enantioselectivities (90-99% ee). According to the results of nonlinear effect studies, deuterium-labeling experiments, and DFT calculation investigations, a reasonable catalytic mechanism for this nickel-catalyzed asymmetric hydrogenation was provided, which displayed that the two added hydrogen atoms of the hydrogenation products could be from H2 through the insertion of Ni-H and subsequent hydrogenolysis.

Nickel-Catalyzed Chemoselective Asymmetric Hydrogenation of α,ß-Unsaturated Ketoimines: An Efficient Approach to Chiral Allylic Amines.

An efficient synthetic route to chiral allylic amines has been developed by nickel/(S,S)-Ph-BPE complex catalyzed chemoselective asymmetric hydrogenation of α,ß-unsaturated ketoimines. Varieties of α,ß-unsaturated ketoimines have been well tolerated in this transformation to give chiral allylic amines with high yields and excellent ee values (up to 99% yield, up to 99% ee). A gram-scale reaction with 0.2 mol % catalyst loading has also been achieved.

Nickel-Catalyzed Desymmetric Hydrogenation of Cyclohexadienones: An Efficient Approach to All-Carbon Quaternary Stereocenters.

Nickel-catalyzed desymmetric hydrogenation has been achieved. With the Ni(OTf)2/(S,S)-Ph-BPE system, a series of γ,γ-disubstituted cyclohexadienones were transformed to the corresponding cyclohexenones with a chiral all-carbon quaternary center at the γ position in high yields (92-98%) and excellent enantioselectivities (92%-99% ee). This catalytic system can also tolerate the desymmetric reaction of spirocarbocyclic cyclohexadienones to produce the corresponding cyclohexenones bearing a chiral spiro quaternary carbon with high yields (94%-98%) and ee values (96%-99% ee). Furthermore, this methodology provides an efficient and concise synthetic route to the intermediate of natural products cannabispirenones A and B.

Nickel-Catalyzed Asymmetric Hydrogenation of Cyclic Sulfamidate Imines: Efficient Synthesis of Chiral Cyclic Sulfamidates.

Chiral cyclic sulfamidates are useful building blocks to construct compounds, such as chiral amines, with important applications. Often these compounds can only be generated through expensive precious metal catalysts. Here, Ni(OAc)2/(S, S)-Ph-BPE-catalyzed highly efficient asymmetric hydrogenation of cyclic sulfamidate imines was successfully developed, affording various chiral cyclic sulfamidates with high yields and excellent enantioselectivities (up to 99% yield, >99% enantiomeric excess [ee]). This Ni-catalyzed asymmetric hydrogenation on a gram scale has been achieved with only 0.1 mol% catalyst loading in 99% yield with 93% ee. Other types of N-sulfonyl ketimines were also hydrogenated well to obtain the corresponding products with >99% conversion, 96%-97% yields, and 97%->99% ee. In addition, this asymmetric methodology could produce other enantioenriched organic molecules, such as chiral ß-fluoroamine, amino ether, and phenylglycinol. Moreover, a reasonable catalytic cycle was provided according to the deuterium-labeling studies, which could reveal a possible mechanism for this Ni-catalyzed asymmetric hydrogenation.

Synthesis of Chiral ß-Borylated Carboxylic Esters via Nickel-Catalyzed Asymmetric Hydrogenation.

The highly efficient Ni-catalyzed asymmetric hydrogenation of ß-boronic ester substituted-α,ß-unsaturated carboxylic esters was successfully developed using ( S, S)-Ph-BPE as the ligand. A series of chiral ß-borylated carboxylic esters were obtained with high yields (94%-99% yields) and excellent enantioselectivities (89%-99% ee). The gram-scale asymmetric hydrogenation with a low catalyst loading (0.25 mol %) and synthetic transformation of hydrogenation product demonstrated the great synthetic utility of this methodology.

A cheap metal for a challenging task: nickel-catalyzed highly diastereo- and enantioselective hydrogenation of tetrasubstituted fluorinated enamides.

Nickel-catalyzed asymmetric hydrogenation of challenging tetrasubstituted fluorinated enamides has been achieved, affording chiral α-fluoro-ß-amino esters in high yields with excellent diastereo- and enantioselectivities (up to 98% yield, >99 : 1 dr, up to >99% ee). Deuterium-labeling experiments and control experiments were conducted to probe the mechanism, and the results indicated that the acidity of the solvent plays a critical role in the control of diastereoselectivity by trapping the adduct of nickel hydride to C[double bond, length as m-dash]C bonds via protonolysis, giving the hydrogenation product with stereospecific syn-selectivity. This protocol provides efficient access to chiral α-fluoro-ß-amino esters which have important potential applications in organic synthesis and medicinal chemistry.

Nickel-Catalyzed Highly Enantioselective Hydrogenation of ß-Acetylamino Vinylsulfones: Access to Chiral ß-Amido Sulfones.

The nickel/( S)-Binapine complex was found to be an efficient catalyst for asymmetric hydrogenation of ß-acetylamino vinylsulfones to afford chiral ß-Amido sulfones with excellent yields and enantioselectivities (up to 95% yields and >99% ee). This protocol has good compatibility with a series of substituted ( Z)-ß-acetylamino vinylsulfones or Z/ E isomeric mixtures. A gram-scale reaction has also been achieved in the presence of a 0.2 mol % catalyst loading.

Nickel-catalyzed asymmetric hydrogenation of ß-acylamino nitroolefins: an efficient approach to chiral amines.

An efficient approach for synthesizing chiral ß-amino nitroalkanes has been developed via the Ni-catalyzed asymmetric hydrogenation of challenging ß-amino nitroolefins under mild conditions, affording the desired products in excellent yields and with high enantioselectivities. This protocol had good compatibility with the wide substrate scope and a range of functional groups. The synthesis of chiral ß-amino nitroalkanes on a gram scale has also been achieved. In addition, the reaction mechanism was elucidated using a combined experimental and computational study, and it involved acetate-assisted heterolytic H2 cleavage followed by 1,4-hydride addition and protonation to achieve the nitroalkanes.

Nickel-Catalyzed Enantioselective Hydrogenation of ß-(Acylamino)acrylates: Synthesis of Chiral ß-Amino Acid Derivatives.

The nickel-catalyzed asymmetric hydrogenation of ß-(acylamino)acrylates has been developed, affording chiral ß-amino acid derivatives with excellent yields (95-99% yield) and enantioselectivities (97-99% ee). With the Ni-Binapine system, high enantioselectivities (98-99% ee) have also been obtained in the hydrogenation of Z/E isomeric mixtures of ß-alkyl and ß-aryl ß-(acylamino)acrylates. The synthesis of chiral ß-amino acid derivatives on a gram scale has also been achieved with 0.2 mol % catalyst loading.

Enantioselective Nickel-Catalyzed Mizoroki-Heck Cyclizations To Generate Quaternary Stereocenters.

The development of enantioselective carbon-carbon bond couplings catalyzed by nonprecious metals is highly desirable in terms of cost efficiency and sustainability. The first nickel-catalyzed enantioselective Mizoroki-Heck coupling is reported. This transformation is accomplished via mild reaction conditions, leveraging on QuinoxP* as a chiral ligand to afford oxindoles containing quaternary stereocenters. Good reactivity and selectivity are observed in the presence of various functional groups. Computational studies suggest that the oxidative addition assembles an atropisomeric intermediate responsible for the facial selectivity of the insertion step.

Enantioselective and Diastereoselective Construction of Chiral Amino Alcohols by Iridium-f-Amphox-Catalyzed Asymmetric Hydrogenation via Dynamic Kinetic Resolution.

The iridium-f-amphox-catalyzed asymmetric hydrogenation of racemic α-amino ß-unfunctionalized ketones proceeds via a DKR (dynamic kinetic resolution) process for the construction of various chiral N,N-disubstituted α-amino ß-unfunctionalized alcohols in quantitative yields with excellent enantioselectivities and diastereoselectivities (all products >99% ee and >99:1 dr, TON up to 100 000). Importantly, this catalytic asymmetric hydrogenation with a DKR process provided a highly efficient and powerful synthetic strategy for the preparation of key chiral intermediates of the preclinical antitumor agent (S,S)-R116010.